Achilles tendon: functional anatomy and novel emerging models of imaging classification

Abstract

Purpose Ideally, a classification should have some prognostic value, and should therefore include precise information upon extent and location of the Achilles tendon disorders. We propose a new imaging and anatomical system to classify Achilles tendon disorders at imaging using US and MRI. Approach We consider the non-insertional region as the tendon mid-portion, and distinguish the insertional component into a pre-insertion site, located about two centimetres above the calcaneum, and a calcaneal insertion, where the tendon is attached to the bone. On sagittal scans, we introduced a new classification which considers two main portions: "musculotendinous" and "insertional". In the context of the muscolotendinous portion, it is possible to find muscle fibres proximally, and the free tendon distally. This latter is made up of proximal, middle and distal portions. We also propose a 5 grade Doppler classification system to quantify blood flow, in which Grades I and II are respectively characterised by the presence of one and two vessels within the tendon; in Grades III, IV and V, the neovascularisation respectively involves less than 50 %, from 50 to 90 %, and more than 90 % of the tendon tissue. These proposed systems will require validation and possible modification to be applied to different tendons.

Ultrasonography and Low-field Magnetic Resonance Imaging of the Common Calcanean Tendon in a Rabbit Model for Tendinopathy Research: a Descriptive Study of Normal Anatomy

“…However, there is still no consensus as to which of these modalities is more sensitive and reliable in evaluating the particular pathologies of the calcaneal tendon and predicting clinical outcome. In recent years, imaging techniques have developed dynamically, thus providing high-resolution sonography and high field strength MRI coupled with the introduction of doppler and contrast enhanced imaging as well as new sequences based on ultrashort echo times (Filho et al 2009, Genovese et al 2011, Del Buono et al 2013). In our study we used a veterinary dedicated MRI unit and a standard linear-array orthopaedic ultrasound probe, both of which are easily accessible to a wide range of researchers.…”

“…This protocol was determined not only based on significant contribution of these tendons to the common calcanean tendon but also according to their applicability in tendinopathy research in a rabbit model (Young et al 1998, Oryan et al 2012. Sonograms and scans were assessed qualitatively with a description of normal appearance of elements analogical to those assessed in human Achilles tendon pathologies, that means echogenicity or signal intensity (depending on imaging technique) of the tendon, musculotendinous junctions, the region of calcaneal insertion, the paratenon, the pre-Achilles fat pad and the bursa of calcaneal tendon (Kamel et al 2003, Bleakney and White 2005, Harris and Peduto 2006, Leung and Griffith 2008, McGonagle et al 2008, Pierre-Jerome et al 2010, van Dijk et al 2011, Del Buono et al 2013). Morphometry of the common calcanean tendon was performed on longitudinal sonograms and sagittal T1-weighted MRI (magnetic resonance imaging) scans presenting median section of the crus.…”

“…According to the Chan classification (Del Buono et al 2013), the calcaneal tendon in humans could be divided into musculotendinous and insertional (calcaneal) portions. Adopting this classification to the rabbit model, the musculotendinous component of the common calcanean tendon consisted of the intramuscular part, corresponding to the tendinous plates of the gastrocnemius and the superficial digital flexor, and the free tendon.…”

“…Despite recent advances in the treatment protocols, their outcomes are still unpredictable due to the decreased mechanical properties of fibrovascular scarring and the degenerative nature of many tendon disorders (Kader et al 2002, Shapiro et al 2015. It has been stated that the calcaneal tendon (Achilles tendon) is one of the most frequently injured tendons in the human musculoskeletal system (Pierre-Jerome et al 2010, Del Buono et al 2013). Due to the complexity of tendon injury and the healing processes as well as differences among particular tendinopathic conditions, animal models are essential for addressing fundamental questions in tendon research (Thomopoulos et al 2015).…”

“…Experimental models used to investigate various treatment protocols are usually evaluated by means of histopathological, biochemical or mechanical examinations. However, in practice, diagnostic imaging along with clinical examination are commonly applied for the calcaneal tendon assessment (Bleakney and White 2005, Harris and Peduto 2006, Pierre-Jerome et al 2010, Del Buono et al 2013). Ultrasonography and magnetic resonance imaging provide a non-invasive assessment of tendons, allowing on defining stage of the extend and severity of the disease and evaluation of applied treatment effectiveness.…”